Aerodynamic flameholder



y 1960 s. J. MARKOWSKI 2,938,344

AERODYNAMIC FLAMEHOLDER Filed May 22, 1957 F/GJZ F/G.3.3

3 Sheets-Sheet 3 9.2 fi fi WWI FT l l OOOOOO IN VE N TOR STANLEY J. MAR/(OWS/(l arm? ATTOANE Y United Stats Patent AERODYNAMIC FLAMEHOLDER Stanley J. Markowski, East Hartford, Conn., assignor to United Aircraft Corporation, East Hartford, Conn, a corporation of Delaware 7 Filed May 22, 1957, Ser. No. 660,865

Claims. (Cl. 60-39.72)

This invention relates to supporting combustion and more particularly to providing stagnant areas in gas passages in which combustion may be supported by the use of devices such as fiameholders.

In the past, fiameholders have been used to permit stabilized combustion in gas passages such as the afterburners of aircraft jet engines and these flame-holders normally consisted of trough-like objects placed in the gas flow path and have the disadvantage that the flame actually touches the metallic parts of the flameholder, there is a high velocity gradient between the region immediately behind the flameholder and the region immediately outboard thereof and uncontrolled turbulence occurred. Further, this type of flameholder presents substantial blockage to gas flow.

It is an object of this invention to provide a flameholder which will permit gas to pass therethrough and, therefore, not provide a positive block to gas flow.

It is a further object of this invention to provide a flameholder in which there will be but a small velocity gradient between the initial point of burning and the area adjacent thereto.

It is a further object of this invention to provide a flameholder in which no metallic part will come into contact with either the flame or the hot gases of combustion and in which, in fact, a cool gas path will flow over all metallic parts.

It is a further object of this invention to provide a flameholder which will provide a stagnation point downstream thereof at a predictable point and which will provide a gas reverse flow region of controllable size downstream of the stagnation point.

ice

an aerodynamic flameholder which is capable of controlling the location of the stagnation point and the size of the reverse flow area.

It is a further object of this invention to provide a flameholder in which the unburned gases are in contact with the piloting reverse gas flow region for a substantially increased period of time and over a substantially increased area as compared to conventional flameholders.

It is still a further object of this invention to provide a flameholder in which turbulence can be controlled between the normal level to a very high level and further, such that the turbulence can be localized to the immediate region of initial burning.

It is still a further object of this invention to provide a flameholder which is aerodynamic in nature and which performs the function of first warping the thru-velocity of the gas passing through the flameholder such that it is minimum at the center or along the cross sectional axis of the flameholder and increases on each side thereof to be maximum at points farthest from the flameholder center or cross sectional axis to form either a smooth or stepped aerodynamic trough, with or without spin velocity, then diffusing the gas passing through the flameholder to further reduce gas velocity to a degree where a stagnation point is produced at the flameholder center section and then further diflusing the gas passing through the flameholder to further reduce the Other objects and advantages will be apparent fro the following specification and claims, and from the accompanying drawings which illustrate an embodiment of the invention.

In the drawings:

Fig. l is a showing of an afterburner of the type used on modern aircraft turbojet engines, partially broken away to show the aerodynamic flameholder taught in this application.

Fig. 2 is a cross-sectional showing of my aerodynamic flameholder utilizing gas fiow turning cascades and illustrating the stagnation point, flow reverse area and flame front.

Fig. 3 is a view taken along line AA of Fig. 2 to illustrate corotational cascades.

Fig. 4 is a view taken along line B--B of Fig. 2 to illustrate corotational cascades.

Fig. 5 is a view taken along line C-C of Fig. 2 to illustrate corotational cascades.

Fig. 6 is a view taken along line D--D of Fig. illustrate corotational cascades.

Fig. 7 is a view taken along line AA of Fig. 2 to illustrate counter-rotational cascades.

Fig. 8 is a view taken along line B-B of Fig. illustrate counter-rotational cascades.

Fig. 9 is a view taken along line C-'C of Fig. illustrate counter-rotational cascades.

Fig. 10 is a view taken along line D--D of Fig. 2 to illustrate counter-rotational cascades.

Fig. 11 represents the thru-fiow (C velocity profile or distribution at station'2-2 in Fig. 2 illustrating a uniform velocity change and the aerodynamic trough.

Fig. 12 represents the spin velocity ((1,) or tangential velocity profile at station 2--2 of Fig. 2 for counterrotational cascades.

Fig. 13 represents the spin velocity (C or tangential velocity profile at station 2-2 of Fig. 2 for corotational cascades.

Fig. 14 is a thru-fiow (C velocity distribution or profile at station 3-3 of Fig. 2 illustrating the formation of the stagnation point and the low thru-fiow velocity radient adjacent thereto.

Fig. 15 represents the thru-fiow (C velocity distribution or profile at station 44 of Fig. 2 to illustrate the formation of a reverse flow area downstream of the stagnation point.

Fig. 16 is a cross-sectional showing of my aerodynamic flameholder utilizing a plurality of vaned cascades.

Fig. 17 is a showing along line 1717 of Fig. 16.

Fig. 18 is a showing along line 1818 of Fig. 16.

Fig. 19 illustrates the thru-flow (C velocity profile at station 66-66 of Fig. 16 to show a stepped velocity profile or aerodynamic trough.

Fig. 20 is a cross-sectional showing of my aerodynamic flameholder using a greater plurality of vaned cascades.

Fig. 21 represents the velocity profile at station 70-70 of Fig. 20 to illustrate a stepped velocity profile having a greater number of steps than is illustrated in Fig. 19.

Fig. 22 is a cross-sectional showing of my aerodynamic flameholder utilizing flow resistant gas passages performing the function of varying the thru-flow (C velocity profile as illustrated in Fig. 21.

Fig. 23 is a schematic showing of one of the flow resistant gas passages or resistance grid utilized in the configuration shown in Fig. 22.

Fig. 24 is a cross-sectional showing of my aerodynamic llzuneliolder utilizing a sudden expansion passage to change or warp thru-fiow velocity profile.

Fig. 25 is a showing along line 25-25 of Fig. 24.

Fig. 26 is an illustration ofthe thru-flow (C velocity profile taken at station 100-100 of Figure 24.

Fig. 27 is a cross-sectional showing of my aerodynamic fiameholder utilizing flow resistant gas passages and/or varied cascades in combination with a conventional flameholder trough.

Fig. 28 is a showing of the thru-fiow (C velocity profile at station 108-108 of Fig. 27.

Fig. 29 is a cross-sectional showing of my aerodynamic fiameholder which is designed to be unsymmetrical to alter the position of the stagnation point and reverse gas flow area.

Figs. 30 and 31 are end views of portions of my aerodynamic flameholder of the flow resistant passage type to show the pattern of high velocity and low velocity passages.

Fig. 32 is an end View of the flameholder shown in Fig. 2 and is taken along line 32-32. Purely for illustration purposes, a straight flameholder with corotating, uniform twist change vanes is shown.

Fig. 33 is an end view of the flameholder shown in Fig. 16 and is taken along line 33-33. Purely for illustration purposes, a straight fiameholder is shown.

Fig. 34 is an end view of the flameholder shown in Fig. 20 and is taken along line 34-34. Purely for illustration purposes, a straight fiameholder is shown.

Fig. 35 is an end view of the flameholder shown in Fig. 22 and is taken along line 35-35. Purely for illustration purposes, a straight flameholder is shown.

Fig. 36 is an end view of the fiameholder shown in Fig. 24 and is taken along line 36-36. Purely for illustration purposes, a straight fiameholder is shown.

Fig. 37 is an end view of the flameholder shown in Fig. 27 and is taken along line 37-37. Purely for illustration purposes, a straight fiarneholder is shown.

For purposes of simplification and to illustrate a complete and workable embodiment, this invention will be described with respect to a flameholder for use in a gas passage through which gas flows, such as the afterburner of a modern aircraft turbojet engine. It is the function of such an afterburner to create a region capable of supporting combustion within the gas passage without detrimentally blocking gas fiow through the passage. If a fiameholder were not used in an afterburner duct, any flame ignited therein would be blown through the duct and discharged into the atmosphere. The flameholder must create a stagnant region in which ignition and combustion can occur.

It should be borne in mind that the shape of the flameholder unit 20 is immaterial to this invention as the flameholder unit 20 may comprise one or more annular rings, or radially projecting spokes projecting from the afterburner. centerline radially outward toward the afterburner walls, a star-shaped frame, a helix, or any other designed configuration which may lie in a single radial plane with respect to the after-burner or be staggered axially along the afterburner centerline.

Referring to Fig. 1, we see afterburner which is located downstream of and receives the exhaust gas discharges from the modern aircraft jet engine of the type disclosed in United States Patent No. 2,770,946. Afterburner 10 is substantially a gas passage, preferably of circular cross section, and defined by or contained within afterburner duct or wall 12. Afterburner duct 12 is symmetrical above afterburner centerline or axis 14. Afterburner 10 may be provided with an exhaust nozzle 16 which is used to vary the discharge area through which the gases passing through afterburner 19 must be exhausted. Exhaust nozzle 16 is actuated by any convenient actuating means such as hydraulic cylinder and piston unit 18. Flameholder 20 is located in afterburner 10 and serves the function of creating a stagnant area or region of gas fiow velocity less than flame speed downstream thereof in which combustion may be supported. Fuel may be introduced into afterburner 10 by any convenient means such as fuel spray bar 22, through which fuel is sprayed in atomized form into afterburner 10. Any convenient means, such as spark plug 24, an explosive charge, or a streak of igniting fuel discharged from the engine may be used to ignite the fuel air mixture located within stagnant region 26 downstream of flameholders 20. Ignition and combustion of the fuel air mixture occurs in stagnation region 26.

The flameholder taught therein will be defined as an aerodynamic fiameholder because gas is passed both through and around the flameholder unit and the flameholder is of such a configuration that it first changes the velocity profile of the gas passing through the flameholder to form an aerodynamic trough, that is, to change the velocity profile such that it is minimum at its center or along the flameholder cross-sectional axis and progresses either uniformly, or otherwise to become maximum at the farthest point at each side of the center or flameholder cross-sectional axis, then difiusing the gas being passed through the flameholder to cause further velocity reduction so that a stagnation point is formed at a point down-.

stream of the previously mentioned minimum velocity region, then further diffusing this exhaust gas so that a region of reverse gas flow is formed downstream of the stagnation point. The stagnation point provides excellent fuel-air ignition qualities and, together with the reversed gas flow area, provides excellent combustion supporting qualities.

While the areodynamic fiameholder taught herein may be accomplished in several different ways, for purposes of description at vaned cascade type and a flow resistance type will be stressed mainly.

Referring to Fig. 2, we see a cross section of flameholder 29. The cross section would be as shown without respect to the over-all shape of the flameholder, whether it be annular or of the other configuration enumerated supra. Flameholder 20 comprises two main parts, the first being velocity Warping or changing section 30 and the second being diffusing section 32. Air enters fiameholder 20 and passes first through velocity altering section 30 and then through diffuser section 32, from which it is discharged into stagnation area 26. Velocity warping area 30 is shown to consist of a separator plate 34 and an outer cascade of vanes 36 on one side thereof and an inner cascade of vanes 38 on the other side thereof. It is a characteristic of the blading used in cascades 36 and 38 that the degree of gas flow warping or turning caused by the blade contouring increases from walls 40 and 42 toward separate plate 34, such that maximum warpage or flow turning occurs in the vicinity of the separator plate 34. Cascades 36 and 38 may be shaped for co-rotation, in which case the vane stations taken along lines A-A, B-B, C-C, D-D are shown in Figs. 3 through 6 respectively. When cascades 36 and 38 are designed for counter-rotation, the vane stations A-A, B-B, C-C, D-D are shown in Figs. 7 through 10, respectively. The vane cascades 36 and 38 perform the function of warping the gas flow or turning the gas ftow so as to alter the so-called thru-fiow velocity dis tribution to be minimum along the cross-sectional axis 44 of fiameholder 2t) and increasing on each side thereof, whether symmetrically, uniformly or otherwise to become maximum at the farthest points on each side of axis 44, as shown in Fig. 11,-which'is taken along plane 2-2 of Fig. 2. As used herein the term thru-velocity means a gas velocity passing through fiarneholder 20 in' a direction parallel to axis 4-4, and known as C as opposed to tangential or spin velocity, known as C which flows in a plane perpendicular to axis 44. In installations where the vanes of cascades 36 and 38 are twisted uniformly, the thru-fiow velocity profile will boas shown in Fig. 11, to uniformly vary from minimum to maximum progressively on each side of the axis or separator plate 34. Steps can be accomplished in the thruflow velocity profile by using vanes in cascades 36 and 38 which are not twisted uniformly but which are made up of sections with distinct and varying degrees of twist. The thru-flow (C velocity distribution or profile is made to form an aerodynamic trough 46 (Fig. 11) which is convex with respect to flameholder portion 30 or due to the different degrees of twist or velocity warping accomplished at the various stations of the vanes in cascades 36 and 38. Fig. 12 illustrates the spin velocity (C distribution or profile at station 2-2 of flameholder 20 when cascades 36 and38 are counter-rotating configurations, whereas Fig. 13 illustrates this spin velocity profile at station '2-2 whencascades 36 and 38 are of corotating configuration.

After the gas passing through flameholder 20 achieves the thru-fiow velocity profile shown in Fig. 11 at station 2-2 it is then diffused in section 32 between stations 2-2 and 3-3 such that velocity reduction occurs due to diffusion so that at station 33 the thru-flow (C velocity profile is as illustrated in Fig. 14, in which the flow at point 48 is of zero velocity with small velocity gradients on each side thereof so that stagnation point 48 is formed at station 3-3, substantially on axis 44. By proper area selection, flameholder 20 can be designed so that stagnation point 48, which is stagnant or essen-. tially so, only occurs and so that no or but a small reverse gas flow area, described hereinafter occurs.

In passing between stations 33 and 4-4 of diffuser section 32 the gas is further difiused, bringing about a further velocity reduction and change such that at station 44 of Fig. 2 the thru-fiow (C velocity profile is as shown in Fig. 15, such that there are areas of positive flow 50 and 52 external of an area of reversed flow 54, such that a reversed flow region 54 occurs downstream of stagnation point 48 and is substantially symmetrical about axis 44, as shown in Fig. 2.

It will be noted in referring to Fig. 2, with respect to the velocity profile shown in Fig. 11, that there is always gas or air flow in a downstream or positive direction passing through and downstream beyond section 30 or cascades 36 and 38. This positive flow prevents the flame or hot gases of combustion which will be taking place in reverse gas flow region 54 from moving upstream to come in contact with the parts of cascades 36 and 38. Further, the air being diifused through difiuser section 32 is passed along the walls 40 and 42 of the diffuser, thereby defining the boundaries of the flame front 60 to be roughly in the position shown in Fig. 2. The positive air flow through and beyond cascades 36 and 38 plus the air fiow along walls 40 and 42 of diffuser section 32 serves the functions of cooling all parts of flame holder 20 and preventing either the flame or the hot gases of combustion generated within the combustion zone 26, including reverse gas flow area 54, from coming into contact with the parts of flameholder 2! As mentioned previously, a uniformly varying thrufiow (C velocity profile can be obtained at station 22 of Fig. 2, as illustrated in Fig. 11, by providing vanes in cascades 36 and 38 which are of uniform twist. Further, stepped thru-flow (C velocity profiles may be attained at station 22 of Fig. 2 by fabricating the vanes of cascades 36 and 38 such that there will be a plurality of stations of varying degrees of twist as opposed to a uniform twist. The varying twist stationed vanes will be fabricated with the stations of maximum twist adjacent to separator plate 34 and with stations of progres- 'sively lesser twist on each side of separator plate 34 culminating in stations of minimum twist adjacent to walls 40 and 42. It may be desirable, possibly for purposes of fabrication, to attain the stepped thru-flow (C velocity profile by providinga plurality of cascades in excess of two, such as the quadruple cascade unit shown in jFig. 1 6 in which the vanes of the exterior cascades 6 62 and are substantially streamlined struts and the vanes of cascades 36 and 38 are twisted to a greater degree either for co-rotation as described in connection with Fig. 2 or for counter-rotation as illustrated in Figs. 17 and 18. The stepped thru-flow (C velocity profile shown in Fig. 19 will be obtained at station 66 of Fig. 16 by passing gas or air through aerodynamic flameholder 20 of Fig. 16.

If a greater number of steps are desired in the (C velocity profile, a construction of the type shown in Fig. 20 may be used. Fig. 20 is representative of a crosssectional showingof an aerodynamic flameholder which utilizes a plurality of vaned cascades with maximum vane twist along the cross-sectional axis 44 of the flameholder 20 and diminishing on each side thereof to be of minimum twist along walls 40 and 42. In Fig. 20 the twist of the vanes of cascade 68 is greater than the twist in the vanes of cascades 36 and 38, which are, in turn, vanes of greater twist than those in cascades 62 and 64. Fig. 21 illustrates the thru-fiow 0,. velocity profile obtained at station 70--70 of Fig. 20, which is minimum'along cross-sectional axis 44 and maximum along walls 40 and 42 to form a stepped aerodynamic trough along line 72 of Fig. 21. It will be obvious that any number of cascades, utilizing co-rotational or counter-rotational vanes, may be used in this fashion,

To this point my aerodynamic flameholder has been described in relation to vane cascade units which warp or turn the gas which passes through section 30 of flameholder 20 to provide a thru-flow (C velocity profile such that it is minimum along the flameholder cross-sectional axis 44 and increases on each side thereof to form an aerodynamic trough prior to diffusion. In the flameholder using cascades, the thru-flow velocity is changed, but at the same time a tangential (C spin velocity is formed. The tangential or spin velocity (C is sometimes considered to be undesirable. To avoid the for; mation of spin velocity and yet effect a thru-flow velocity profile of the type described supra, a flow resistance type of aerodynamic flameholder may be used. This flow resistance type of flameholder is depicted in Fig. 22 in which frictional or flow resistance units 74 are substituted for cascades 36 and 38 thru-fiow velocity profile changing section 30 for use with diffuser section 32. The centrally located flow resistance passage 76 of Fig. 22 is shown to be symmetric about cross-section axis 44 and is designed to be of the configuration shown in Fig. 23 to provide a greater resistance to flow than do flow resistance units 78 and 80 which are located outboard of the central unit 'with'respect to axis 44. While additional flow resistance units may be used external of the units 78 and 80, and the flow resistance of the resistance units should decrease in a direction outboard of axis 44, air foil struts 82 are used in the installation shown in Fig. 22. The friction or flow resistance units shown in Fig. 22 will provide the same type of thru-flow (C velocity profile as is shown in station 8484 as is shown in Fig. 21 and provided by the cascade configuration shown in Fig. 20. It will be obvious that two similar high flow resistant passages, such as 76, could be used in Fig. 22 and abut along axis 44. Further, while the flow resistance type flameholder normally gives stepped thru-flow (C velocity pro-files without spin velocity (C the number of resistance passages may be increased to a point where the profile is substantially uniform.

The theory of operation in utilizing resistance units or grids such as 76 is to pass the gas flow through a small chamber 86 to dissipate the total gas pressure by increas-. ing the velocity of the gas fiow and then passing the gas through a difiuser or expansion unit 88 to reduce the velocity. The amount of thru-flow velocity (C attained along station 8484 varies as the amount of total pres sure reduction effected in resistance chambers such as 76, 7s and s0. 1 f f After passing station 8484 of the resistance-type aerodynamic fiameholder 20 shown in Fig. 22, the gas is then passed through diffuser section 32 and, acts in the same fashion described with respect to stations 3-3 and 44 of Fig. 2 to form a stagnation point and a reverse fiow area downstream thereof as shown in Fig. 2.

In addition to the cascade and flow resistance type of aerodynamic flameholders, Fig. 24 illustrates another flameholder configuration in which the thru-flow (C velocity is altered as shown in Fig. 26 by first passing the fiameholder gas through sudden expansion passage 90 which is located along a cross section lin 44 of flameholder 20 and also passing gas through passages of less fiow restriction 92 and 94 which are located outboard of sudden expansion passage 90 and center line 44. To gain entrance into sudden expansion passage 90, the gas must pass through an area of restriction such as the holes 96 located in plate 98. After passing through passages 90, 92, and 94 the thru-fiow velocity at station 100-100 will be as shown in Fig. 26. Sudden expansion passage 90 performs the function of destroying the total pressure of the gas passing therethrough so as to reduce its velocity. Diffuser 32, as used in the configuration as shown in Fig. 24, acts in the same way as described for Fig. 2 and Fig. 22.

It should be borne in mind that the flow resistance type of fiameholder can be used in combination with the vane cascade type of fiameholder as each performs the function of warping or changing thru-flow (C velocity as described supra.

Further, the flow resistance type or the vane cascade type of aerodynamic flameholder, or a combination thereof, can be used with a conventional trough type of flameholder as shown in Fig. 27. In Fig. 27, flameholder 20 comprises central resistance passage 76, adjacent resist ance means or passages 78 and 80 and vane cascades 36 and 38, all of which are enclosed within support rings 102 and 104 and which are located upstream of trough type fiameholder 106 to form a thru-fiow (C velocity profile as shown in Fig. 28 along line 108-408 of Fig. 27. Obviously, if we wish to avoid any spin velocity, (C the usual twisted vane is not used but non-twisted vanes are used in the cascade or flow resistance passages.

Experience has shown that due to gas centrifugal forces acting on flameholder 20 the position of the reverse flow region 54 will be shifted away from cross-sectional centerline 44. To avoid this, a non-symmetrical aerodynamic flameholder unit 20 of the type illustrated in Fig. 29 may be used. It will be noted that inner Wall 110 differs in axial dimension from outer wall 112 and that lower cascade 114 differs from upper cascade 116. By varying the wall and/or cascade size and/or shape, the position of stagnation point 48 and reverse flow region 54 may be shifted with respect to cross-sectional axis 44.

-It has been found desirable to shape the entrance of the flow resistance passages such as 86 so as to deflect particles which may be in the gases entering the flameholder and it has further been found desirable to select the position of the high velocity flow resistance passages such that they envelope or surround the low velocity flow resistance passages, regardless of the shape of the flame holder. Fig. 30 represents a cross section view through the resistance passages of a fiameholder having a substantial T-shaped junction. The high velocity passages are designated as H and it will be noted that they envelope or surround the low velocity passages which are designated as L.

Fig. 31 illustrates the envelope positioning of the high velocity passages with respect to the low velocity passages in flameholder construction which end abruptly, such as those which comprise radially extending flameholders. In both Figs. 30 and 31 the area designated as D represents the diffusion area 32 downstream of the flow resistance section 74.

Some of .the advantages gained by using the aerodynamic flameholders taught herein instead of the conventional flameholders, beyond reductions in flow blockage and weight, will now be discussed.

The thru-fiow (C velocity gradient at the point of initial burning will be greatly reduced with respect to the velocity gradient encountered in a conventional flameholder. This is illustrated in Fig. 14 since stagnation points 48, which will be the point of initial burning, and it will be noted that there is a minute velocity gradient on each side thereof and that this velocity gradient changes smoothly and in small degrees throughout the full velocity profile.

As mentioned above, because of the positive flow through the vaned cascades and the flow restriction passages and also because of the gas flow along walls 40 and 42 of the diffuser 32, neither the hot gases nor the flames of combustion come into contact with flameholder parts, as occurs in conventional flameholders.

Actually, flameholder parts are cooled by this gas flow. The aerodynamic flameholder provides a reverse gas flow region which can be controlled as to size and gas velocity, both by proper selection of cascades and/or flow restriction passages, or the combination of the two, and by proper selection of the size and angularity of the diffuser section. It will be noted that the aerodynamic fiameholder accomplishes the unusual phenomenon of causing flow separation beginning at a point centralized within a diffuser.

The aerodynamic flameholder permits control of the length of the path of contact between the unburned gases and the piloting hot reverse flow region or, viewed from another standpoint, provides for the unburned gases to be in contact with the piloting reverse flow region for a greater period of time. This is accomplished by selecting an aerodynamic fiameholder configuration, as de scribed in the preceding paragraph, which will provide a reverse region of the required size contiguous with an immediate region of substantially reduced velocity for the desired result.

In installations where a high degree of turbulence is desired, the use of counter-rotating flow cascades in the aerodynamic fiameholder, or vaned cascades, and/or flow resistant passages which produce sharper velocity gradients, permits changing turbulence from a normal level to a very high level and this turbulence can be localized to the immediate region of initial burning.

While particular configurations have been selected to illustrate the aerodynamic flameholder taught herein, it will be obvious to those skilled in the art that enumerable configurations can be used to accomplish the functions of the aerodynamic fiarneholder, namely, first warping the thru-fiow (C velocity profile to form an aerodynamic trough which is convex when viewed from a point upstream of the flameholder, then diffusing the gas passing through the flameholder to effect gas velocity reductions to form a stagnation point and a reverse flow region downstream of the stagnation point.

It is to be understood that the invention is not limited to the specific embodiments herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

:1. In a fiameholder having a main axis and having a cross-sectional axis spaced from said main axis, means to pass gas through said fiameholder, means for causing the thru fiow velocity profile of the gas passing through said fiarneholder to vary from a minimum to maximum progressively on each side of said cross-sectional axis thereby forming a trough-shaped thru-flow velocity profile in the shape of said flameholder, and means to reduce the speed of said trough-shaped thru-flow velocity profile below flame speed at a location downstream of said flameholder.

2. A duct having an axis, a flameholder located within said duct and surrounding said duct axis and having a cross-sectional axis spaced from said duct axis,

asses-r4 means to pass gas through said duct-and said flameholder, means for causing the thru-flow velocity profile of the gas passing through said flameholder to vary from a minimum to maximum progressively on each side of said cross-sectional axis thereby forming in said duct a troughshaped thru-fiow velocity profile in the shape of said flameholder, and means to reduce the speed of said trough-shaped thru-flow velocity profile below flame speed at a location downstream of said flameholder.

3. A duct having an axis, a flameholder located within said duct and surrounding said duct axis and having a cross-sectional axis spaced from said duct axis, means to pass gas through said duct and said flameholder, means for causing the thru-fiow velocity profile of the gas passing through said flameholder to vary from a minimum to maximum progressively on each side of said crosssectional axis thereby forming in said duct a trough shaped thru-tlow velocity profile in the shape of said flameholder, and means to then dilfuse and thereby reduce the speed of said trough-shaped thru-fiow velocity profile below flame speed to form a series of stagnation points and a reverse gas flow region downstream of said stagnation points both at locations downstream of said flameholder and in the shape thereof.

4. In a flameholder surrounding a main axis and having a cross-sectional axis spaced from said main axis and including a first portion and a second portion downstream thereof, means to pass gas through said flameholder so that said first portion changes the thru-flow velocity profile of the gas passing through said fiameholder to be convex with respect to said first portion and concentric about said cross-sectional axis thereby forming a trough-shaped thru-flow velocity profile in the shape of said flameholder and so that said second portion reduces the speed of said trough-shaped thru-flow velocity profile so the minimum velocity of said profile is below flame speed at a location downstream of said flameholder. V g

5. A duct having an axis, a flameholder located within said duct and surrounding said duct axis and having a cross-sectional axis spaced from said duct axis and including a first portion and a second portion comprising a diffuser downstream thereof, means to pass gas through said duct and said flameholder so that said first portion changes the thru-flow velocity profile of the gas passing through said flameholder to be convex with respect to said first portion and concentric about said cross-sectional axis thereby forming in said duct a trough-shaped thru-fiow velocity profile in the shape of said flameholder and so that said second portion then performs a difiusion function to reduce the speed of said trough-shaped thru-flow velocity profile thereby causingflow separation in said second portion substantially symmetrically about said cross-sectional axis to form a stagnation region substantially on said cross-sectional axis and a reverse gas flow region downstream of said stagnation region both at locations downstream of said flameholder and in the shape thereof.

6. In a flameholder having a main axis and having a cross-sectional axis spaced from said main axis, means to'pass' gas through said duct and said flameholder, gas flow turning means for changing the thru-flow velocity profile of the gas passing through said flameholder to be convex with respect to said fiow turning means and minimum substantially along and substantially symmetric about said cross-sectional axis thereby forming a troughshaped thru-fiow velocity profile in the shape of said flameholder, and means to then dilfuse the gas passing thru said flameholder to reduce the speed of said troughshaped thru-flow velocity profile thereby forming a stagnation region substantially on said cross-sectional axis and a reverse gas flow region downstream of said stagnation region both at locations downstream of said flameholder and in the shape thereof.

7. In a flameholder having a main axis and having a 10 cross-sectional axis spaced from said main axis, means to pass gas through said duct and said flameholder, gas flow resistance means for changing the thru-flow velocity profile of the gas passing through said flameholder to be convex with respect to said flow resistance means and,

and a reverse gas flow region downstream of said stag-v nation region both at locations downstream of said flameholder and in the shape thereof.

8. An afterburner adapted to receive exhaust gases from a jet engine comprising a duct having an axis, an annular flameholder located within said afterburner duct and concentrically surrounding said duct axis and having a cross-sectional axis, means to pass gas through said duct and said flameholder, at least one vaned cascade forming the upstream portion of said flameholder and located on each side of said cross-sectional axis thru which gas is passed to change the thru-flow velocity profile of the gas passing through said flameholder to be convex with respect to said cascade and minimum substantially along and substantially symmetric about said cross-sectional axis thereby forming in said duct a troughshaped thru-flow velocity profile in the shape of said flameholder, said cascades being corotating and means to then diffuse the gas passing thru said flameholder to reduce the speed of said trough-shaped thru-fiow velocity 9. An afterburner adapted to receive exhaust gases from a jet engine comprising a duct having an axis, an

annular flameholder located within said af-terburner duct and concentrically surrounding said duct axis and having a cross-sectional axis, means to pass gas through said duct and said flameholder, at least one vaned cascade forming the upstream portion of said flameholder and located on each side of said cross-sectional axis thru which gas is passed to change the thru-flow velocity profile of the gas passing through said flameholder to be convex with respect to said cascade and minimum substantially along and substantially symmetric about said cross-sectional axis thereby forming in said duct a trough shaped thru-fiow velocity profile in the shape of said flameholder, said cascades being counterrotating and means to then diffuse the gas passing thru sa-id flameholder to reduce the speed of said trough-shaped thrufiow velocity profile below flame speed substantially along said cross-sectional axis to cause gas flow separation substantially along and symmetric about said crosssectional axis to thereby form a stagnation region and a reverse gas fiow region downstream of said stagnation region both at locations downstream of said flameholder and in the shape thereof.

10. A duct having an axis, a flameholder located within said duct and surrounding said duct axis and having a cross-sectional axis spaced from said duct axis, means to pass gas through said duct and said flameholder at high velocity, means comprising a plurality of gas flow restricting passages shaped to provide less fiow restriction as the distance said passages are located from said axis increases to change the thru-fiow velocity profile of the gas passing through said flameholder to be convex with respect to said last-mentioned means thereby form ing in said duct a trough-shaped thru-fiow velocity profile in the shape of said flameholder, which profile is mum substantially along said cross-sectional axis and increases gradually and substantially uniformly on each side thereof, and diverging wall means to then diffuse the gas passing thru said fiameholder to reduce the speed of said trough-shaped thru-flow velocity profile to cause gas flow separation commencing substantially on said crosss ectional axis and increasing substantially symmetrically on each side thereof thereby forming a stagnation region and a reverse gas flow region downstream thereof at locations downstream of said flameholder and in the shape thereof.

11. A duct having an axis, a fiameholder located within said duct and surrounding said duct axis and having a cross-sectional axis spaced from said duct axis, means to pass gas through said duct and said flameholder at high'velocity, means comprising a plurality of gas flow restricting passages shaped to provide less flow restriction as the distance said passages are located from said axis increases and further positioned so that passages of less flow restriction encompass those of greater flow restriction to change the thru-flow velocity profile of the gas passing through said flameholder to be convex with respect to said last-mentioned means thereby forming in said duct a trough-shaped thru-flow velocity profile in the shape of said flameholder, which profile is minimum substantially along said cross-sectional axis and increases gradually and substantially uniformly on each side thereof, and diverging wall means to then diffuse the gas passing thru said flameholder to reduce the speed of said trough-shaped thru-flow velocity profile to cause gas flow separation commencing substantially on said crosssectional axis and increasing substantially symmetrically on each side thereof thereby forming a stagnation region and a reverse gas flow region downstream thereof at locations downstream of said flameholder and inthe shape thereof.

12. A duct having an axis, a flameholder located within said duct and surrounding said duct axis and having a cross-sectional axis spaced from said duct axis, means to pass gas through said duct and said flameholder at high velocity, means including at least one sudden expansion chamber to change the thru-flow velocity profile of the gas passing through said flameholder to be convex with respect to said last-mentioned means thereby forming in said duct a trough-shaped thru-flow velocity profile in the shape of said flameholder, which profile is minimum substantially along said cross-sectional axis and increases gradually and substantially uniformly on each side thereof, and diverging wall means to then diffuse the gas passing thru said flameholder to reduce the speed of said trough-shaped thru-flow velocity profile to cause gas flow separation commencing substantially on said cross-sectional axis and increasing substantially symmetrically on each side thereof thereby forming a stagnation region and a reverse gas flow region downstream thereof at locations downstream of said flameholder and in the shape thereof.

13., A duct having an axis, a flameholder located within said duct and surrounding said duct axis and having a cross-sectional axis spaced from said duct axis, means to velocity, means including at least one vaned cascade and one'flow restricting passage to change the thruflow veloc-' ity profile of the gas passing through said flameholder to be convex with respect to said last-mentioned means thereby forming in said duct atrough-shaped thru-flow velocity profile in'the shape of said flameholder, which profile is substantially along said cross-sectional and increases gradually and substantially uniformly on each side thereof, and diverging wall means to then diffuse the gas passing thru said fiameholder to reduce the speed of said trough-shaped thru-flow velocity profile to cause gas flow separation commencing substantially on said-cross-sectional axis and increasing substantially symmetrically on each side thereof thereby forming a stagnation region and a reverse gas flow region downstream thereof at locations downstream of said flameholder and in the shape thereof.

14. A flameholder having an axis and a cross-sectional axis spaced therefrom and including outer walls, means for passing gas through and around said fiameholder, means for changing the thru-flow velocity profile of the gas passing through the flameholder such that it is minimum substantially along said cross-sectional axis and increases gradually on each side thereof to be maximum at points farthest from said cross-sectional axis, thereby forming a trough-shaped thru-flow velocity profile in the shape of said fiameholder, and a trough-shaped structure located substantially on said axis and downstream of and convex with respect to said velocity profile changing means. w

15. A fia'meholder positioned unsymmetrically about an axis and having a cross-sectional axis spaced therefrom, means for passing gas through said flameholder, means for changing the thru-flow velocity profileof the gas passing through the flameholder such that it is in the shape of said flameholder and minimum substantially along said cross-sectional axis and increases gradually on each side thereof to be maximum. at points farthest from said cross-sectional axis, means including dissimilar walls located on opposite sides of said cross-sectional axis to then diffuse the gas passing through said flameholder to cause reduction of the thru-flow velocity of said gas so profiled thereby forming a stagnation point substantially on said cross-sectional axis and a reverse gas flow region downstream of said stagnation point both at locations remote from both of said means.

References Cited in the file of this patent UNITED STATES PATENTS 2,560,223 Hanzalek July 10, 1951 2,603,949 Brown July 22, 1952 2,664,703 Whitelaw Jan. 5, 1954 2,714,287 Carr Aug. 2, 1955 2,720,754 Francois Oct. I8, 1955- 2,734,560 Harris et a1 Feb. 14, 1956 FOREIGN PATENTS 969,610 France May 24, 1950 619,251 Great Britain Mar. 7, 1949 

